Cosmic Lens Reveals Distant Galactic Violence

By cleverly unraveling the workings of a natural cosmic lens,
astronomers have gained a rare glimpse of the violent assembly
of a young galaxy in the early Universe. Their new picture
suggests that the galaxy has collided with another, feeding a
supermassive black hole and triggering a tremendous burst of
star formation.

The astronomers used the National Science Foundation's
Very Large Array (VLA) radio telescope to look at a galaxy more than
12 billion
light-years from Earth, seen as it was when the
Universe was only about 15 percent of its current age. Between
this galaxy and Earth lies another distant galaxy, so perfectly
aligned along the line of sight that its gravity bends the light
and radio waves from the farther object into a circle, or
"Einstein Ring."

This
gravitational lens made it possible for the scientists to
learn details of the young, distant galaxy that would have been
unobtainable otherwise.

"Nature provided us with a magnifying glass to peer into the
workings of a nascent galaxy, providing an exciting
look at the violent, messy process of building galaxies in the
early history of the Universe," said Dominik Riechers, who led
this project at the Max Planck Institute for Astronomy in
Germany and now is a Hubble Fellow at the California Institute
of Technology (Caltech).

The new picture of the distant galaxy, dubbed PSS J2322+1944,
shows a massive reservoir of gas, 16,000 light-years in diameter,
that contains the raw material for building new stars. A supermassive
black hole is voraciously eating material, and new stars are
being born at the rate of nearly 700 Suns per year. By comparison,
our Milky Way Galaxy produces the equivalent of about 3-4 Suns
per year.

The black hole appears to be near the edge, rather than at the
center, of the giant gas reservoir, indicating, the astronomers say,
that the galaxy has merged with another.

"This whole picture, of massive galaxies and supermassive black
holes assembling themselves through major galaxy mergers so
early in the Universe, is a new paradigm in galaxy formation.
This gravitationally lensed system allows us to see this process
in unprecedented detail," said Chris Carilli, of the National
Radio Astronomy Observatory.

In 2003, astronomers studied PSS J2322+1944, finding the
Einstein Ring by observing radio waves emitted by molecules of
Carbon Monoxide (CO). When astronomers see large amounts of
CO gas in a galaxy, they conclude that there also is a large
amount of molecular Hydrogen present, and thus a large
reservoir of fuel for star formation.

In the latest study, scientists painstakingly produced a physical
model of the lensing intermediate galaxy. By knowing the mass,
structure and orientation of this galaxy, they could then
deduce the details of how it bends the light and radio waves
from the more-distant galaxy. This allowed them to reconstruct
a picture of the distant object. By doing this with multiple
VLA images made at different radio frequencies, they were
able to measure the motions of the gas in the distant galaxy.

"The lensing galaxy was, in effect, part of our telescope.
By projecting backward through the lens, we determined the
structure and dynamics of the galaxy behind it," said Fabian
Walter of the Max-Planck Institute for Astronomy in Germany.

PSS J2322+1944 was first discovered by George Djorgovski of Caltech,
using the digitized Palomar Observatory Sky Survey. Later radio and
optical studies showed that it had a huge reservoir of dust and
molecular gas, and indicated gravitational lensing.

Gravitational lenses were predicted, based on Albert Einstein's
General Theory of Relativity, in 1919. Einstein himself showed in 1936
that a perfectly-aligned gravitational lens would produce a circular
image, but felt that the chances of actually observing such an object
were nearly zero. The first gravitational lens was discovered in 1979,
and
the first Einstein Ring was discovered by researchers using the
VLA in 1987.

Riechers, Carilli, and Walter worked with Brendon Brewer and Geraint
Lewis of the University of Sydney in Australia, Frank Bertoldi of
the University of Bonn in Germany, and Pierre Cox of the Institute
of Millimeter Radio Astronomy in France. The scientists reported
their findings in the October 20 edition of the Astrophysical Journal.